Refractory



atente use it, re

tithiidiiti anraaeroay i. mentschler, Willeughby, Ohio No nr'a.applicants may at, ease.

seen hie. areas This invention relates to refractory bodies con -tainingcarbon and clay and method of produc ing them. Bodies according to theinvention are especially desirable for use where the refractory contactswith molten metals, such as hot tons, linings for ladles, conduits forconveying molten metals in casting operations. Other and widelydiflerent uses are possible and will be readily apparent to thoseskilled in the various arts involving the use of refractories. For useswhere the presence of any carbon is undesirable, the refractory,according to the invention, may take the form of a heat hardenedcarbon-clay refractory having a surface portion of the carbon burnedout. For uses where at least a; small amount of carbon can be tolerated,useful bodies according to the invention may be produced without burningat the surface, such bodies achieving the objects of the invention otherthan protection against contact of carbon with molten metals or othermaterials in contact with the refractory.

Objects of the invention are to produce refractory bodies having poorheat conducting properties, substantial freedom from cracking orspalling when subjected to violent temperature changes, such as would becaused by contact with molten metal, and having ample tensile-andresistance strength, and high inertn'ess toboth carbon and clayattacking substances, while being low in cost and light in weight, andto provide at low cost a surface such as will prevent contact of moltenmetal and other carbon attacking substances with carbon content of therefractory body. A further object is to provide such surface by removalof the carbon from asurface portion of the refractory. v

A still further object is to provide a body capable of being burned toproduce such refractory body and a peculiarly effective method offorming the same. i

It is well known that in the production of fire clay refractories, greatcare must be exercised in drying and firing to avoid cracking or ruptureof the body due to shrinkage in volume of thefire clay. This shrinkageis due, at the beginning, to the removal of adherent moisture and, laterand at higher temperature, to removal of the water of composition. Withcontinued increase in temperature, and beforesubstantial vitrificationof the clay, various chemical changes occur so that unless the dryingand firing are carried out slowly and with great care, the product maybe ruined.

While the drying of fire clay refractories of such dimensions as hottops for ingot casting according to present prevailing practice.requires from one to two weeks, it is an object attained by my inventionto produce refractory bodies of the size of hot tops in from twenty-fourto fortyeight hours. The burning of a fire clay refractory is generallyconsidered complete when an pressing or extruding operations.

increase in temperature does not result in additional shrinkage. it maythen be said .to have attained its maximum shrinkage. A fire clayrefractory, fired to the point of maximum shrinkage, has a considerablecoemcient of thermal err- .pansion and if its outer surface is suddenlyheated or cooled, there is a great tendency to crack or snail. In thecase or refractory bodies according to my invention, the coemcient ofthermal expansion of the body as a whole is low, and, I believe itlargely ii not wholly on tt account, it can be subjected, as indicatedabove, to sudden and violent temperature changes without any cracking orspelling.

it appears that'the coke particles, which are of in cellularconstruction, yield to the expansion of the clay content so as to resultin the low coemcient of expansion of the body as a whole. I have maderough measurements of the coecient of linear expansion and find it to beabout 50% to 20 60% of that of good-grade fire brick and only a littlehigher than the-reported value for pure hard carbon brick.

burning may be done by heating in an oxidizing atmosphere at a hightemperature so that the carbon is oxidized or burned out to a. desireddepth below the surface of the refractory so as to leave only the claycontent of the refractory at its surface for contacting the molten metalor the like. The expression oxidizing atmosphere" is used in the usualsense of "carbon consuming. In practice, I prefer to use a good grade01' hard coke and a highly refractory fireclay of sumcient plasticity togive good coherence in pugging, The term coke is herein used in theordinary sense of a cellular product produced by heating those grades ofsoft coal known as coking coals. The limiting amount of carbon which canbe employed is de termined by the plasticity of the clay. If too muchcarbon be used the mixture becomes unworkable because of the diminishedplasticity. And, it is to benoted that the use of crushed coke in theform of varied sized grains provides a grog which serves the purpose inthis refractory that grog serves in'the manufacture of ordinary firebrick, etc., and at the same time enhances the value of the refractory.The shrinkage of the carbon and'clay mixture during drying and firing isless than that of the clay alone; and articles fabricated in this wayare enabled to withstand sudden changes in temperature without crackingor spalling. Further, coke has the advantage over sand and other'formsof grog in that it does not swell when heated. In fact, the granularcoke particles in this refractory appear to shrink or be compressed whenthe refractory is heated, whereby to cushion the expansion of theremainder of the body which tends to offset the expansion of the claythus producing a body of minimum shrinkage coefficient. the refractorywhich is composed of a bonded mixture of finely divided carbon andfinely divided clay, the clay and carbon afford mutual protection toeach other in the case of, for example, a very common use of therefractory, i. e. in contact with molten steel masses containing a basicslag. The carbon protects the clay from reaction with the slag while theclay protects the carbon from oxidation and absorption by the steel orslag. Actual use has shown that the mixture is mutually protected to aremarkable extent as indicated although the protection is not absolutelyperfect.

I have found that it is better to crush the coke in some form of hammermill than to crush it by rolling because the former operation gives themost angular product. A very satisfactory crushing is one which willresult in a particle size for the coke about as follows:

- Percent by weight 4-mesh to 8-mesh 47 8-mesh to 12-mesh 35 12-mesh todust 18 These proportions may be varied considerably; all or merely apart of the coke may be used or other forms of finely divided carbonsuch as powdered calcined anthracite or hard coal, etc.; but thereshould always be a portion of finely divided carbon and a portion ofgranular coke. The granular portion should not greatly exceed 4- meshsince the result might be an excessively pitted surface after theburning step. When 55 parts by weight of a finely divided plasticrefractory fireclay are mixed with approximately 45 parts by weight ofthe crushed coke, prepared as above, the mixture moistened with water,pugged, formed and burned, I find that the resulting refractory body issubstantially free from expansion or contractions when subjected tosudden changes in temperature, such for example, as occurs when a hottop is contacted by molten metal in pouring an ingot. It is to beunderstood that variations may be made from the conditions andproportions described, that different forms of carbon for the finelydivided portion may be used, and that any clay which is suitable in themanufacture of refractories in general may be employed with more or lessgood results.

It should be pointed out that in such a mixture of crushed coke and claythe larger particles serve to give strength to the body while thesmaller particles of coke or other carbon fill the interstices betweenthe large particles and at the same time coat and are in turn coated bythe finely divided clay so that a very close mixture results. Bodiesprepared as above outlined may be dried very rapidly without showing anycracks whatever and in burning these bodies the temperature can beraised very rapidly without causing any cracks or checks in the finishedbodies. While the drying of clay hot tops and similar refractory bodiesmade by present prevailing practice requires from one to two weeks, ahot In that portion of top prepared by my method can be dried in fromtwenty-four to'forty-eight hours. Care should be exercised in selectingcarbon and clay having little, or no, pyrites or other easily fusible orflexible or fluxing ingredients as these may cause a pitting ofthe'surfaceof the product or deformation of the body in the burningoperation. Also the coke or carbon used should be substantially freefrom volatile matter so that the finished refractory body is practicallynonporous and the clay residue left after the burning out of the carbonat the surface of the body is burned to a smooth finish. In burning thisrefractory in oxi dizing atmosphere, the heat should be raised rapidlyso that the firing may be completed without oxidizing the carbon to toogreat a depth below its surface. If the carbon is oxidized to too greata depth the physical strength of the body is lessened and itscoefficient of expansion and contraction altered.

The ground clay and conditioned carbon are weighed or measured in therequisite proportions and then thoroughly mixed in approximately drycondition after which the necessary quantity of water is added and themixing continued until the mass is uniform. The proportion of water usedshould be high enough that the mixture is extrudible, that is, can becaused to fiow by application of sufliciently high pressure, yet lowenough that, when shaped, it possesse suilicient rigidity to form welland to retain its shape without deformation from handling. A degree ofrigidity too small' to permit handling of theshaped object withoutdeformation is herein termed fluent". In determining the amount of waterrequired it is necessary to take into consideration the initial adheringmoisture contained in the clay and coke as well as the nature of theclay, some clays requiring more moisture than others to develop therequisite plasticity. In practice, using a good average grade of Ohiofireclay containing approximately ten (10) percent of adhering moistureand ground coke with less than two (2) percent of moisture, I have foundthe following proportions very satisfactory where a mixture of adequaterigidity is required to shape such refractories as hot tops, etc.;

Pounds Coke 360 Clay 640 Water 93 When the mass has been thoroughlymixed, it is introduced into the pug mill (preferably one equipped withtwo shafts for better mixing) and the resulting plastic mass is readyfor shaping. It is highly desirable that this plastic mass should besubjected to high pressure so as to force the mixed, finely dividedparticles into intimate contact and into the interstices between andinto the surface follicles of the coke particles. I prefer to shape theobjects by extrusion, since in that way compression and shaping aresimultaneous, but good results can be had if the mix is subjected tohigh pressure and then shaped by tamping or in any desired manner. Thewater content should not be high enough to render the compressionineffective and this limitation'upon the water content is to beunderstoo as a connotation of the term fluent.

When working. this refractory material I have found it very desirable toremove entrained air as much as possible either by the use of rapidcentrifugal whirling orby subjecting the mass to a vacuum before orwhile forming. I have found that, within the range of my experiments,the higher the pressure used in shaping, the slower will be theoxidation of the surface car- "bon during firing, 'so that articlesadequately pressed may be fired to higher temperatures and for longerperiods without excessive burning out pressure to the square inch andfired to about 2300 F. in the same fumace under otherwise identicalconditions, for 16 hours (from start to finish) was oxidized to anaverage depth of I about V inch. Refractory bodies formed under higherpressures and consequently beingable to withstand, in the firings,higher temperatures and longer periods of firing, without excessiveburning out of surface carbon, are denser and physically stronger thanthose formed under lower pressures.

The pugged mass should he introduced into the shaping mechanism in a.single piece otherwise laminations, flaws, crevices, seams or cracks arelikely to result in the finished article. Espe=.

cially is this true where excess pieces fro previously pressed material,perhaps coated with oil films due to lubricant used in such pressing,are introduced into the shaping mold. Excess pressing scraps should berepugged before using. When shaping is promrly done the surface of theobjects formed is smooth and has a very thin surface skin which shows noseams, we or breaks after burning. After the clay and coke have beenpuggedtogether and shaped, they may be dried at room temperature or inany suitable drying oven. When dried, they are burned by raising thetemperature rapidly, to, e. g. from 1800 F. to 2800' F. under oxidizingconditions. If the furnace construction permits, the drying and firingmay be carried out as one operation inasmuch as this material can bedried rapidly without cracking and where drying and firing are recitedherein as separate steps this consolidation of the two low temperaturefor long periods) is not neces- I sary for the production of asatisfactory refractory when same is prepared as outlined above. Theburning operation removes the surface carbon to a depth of V to l or toa greater or less depth depending upon the pressure used in forming, thelength of time, conditions of firing,

kiln atmosphere, etc. and without substantially changing the grossvolume of the refractory body. The conditions are adjusted to secureremoval of the carbon to the desired depth which should be greater orless depending upon the thickness of the body, the strength required,and other reand low coefiicient of expansion (2.0 to 2.5 times 10- perdegreeFJ.

While I may-form a very useful, heat hardened refractory, having most ofthe properties-above described, by heating the mass in a reducing orneutral atmosphere. or by packing inpowdered coke for the burning, avery-important feature is the removal of carbon from the surface ofrefractory bodies while leaving a claylsurfac capable ofexcluding moltenmetal-onetime like from contact with the carbon clay nib-surfaceportion. It is highlydesirable in alt cases where the presence of asmall quantity of carbon would deleteriously affect the materialt'o'bntact with the refractory, particularly where the material ismolten metal which would absorb'carbon; This application is acontinuation in part of my prior application Serial No. 8,047, filedJanuary 23, 1935: of my application Serial No. 25,479, filed June 7,1935; of my applicatlonSerial No. 44,637, filed October 11, 1935; and ofmy application Serial No. 67,913, filed March 9, 1936;

Having thus described claim is:

, 1. {In a process of making a refractory body, the steps of formingsuch body of an intimate mixture, substantially free from volatilematter, of finely divided carbon, granular coke and finely di-' videdclay, drying such body and subjecting it to an oxidizing atmosphere at atemperature of from about l800 F. to about 2800 1 until the carboncontent is removed from an outer portion thereof tofthe desired depth.

2. In a process of making a refractory body, the steps of forming suchbody of an intimate mixture of finely divided carbon, granular coke andfinely divided clay, highly compacting such body, drying it and heatingit at a temperature short of that required to cause substantialvitrification oi the clay content thereof but high enough and for a timesumcient to cause the resulting refractorybody to attain substantiallyits maximum shrinkage and exhibit high strength and low coeficient ofexpansion.

3. In a process of making a refractory body, the

steps of forming such body of a mixture, substantially free fromvolatile matter, of finely divided my invention, what I' carbon,granular coke and-finely divided clay,-

- highly compacting such bodyf-dryin'g it; and sub- Jecting it to atemperature of from about 1800", F. to about 2800 F. for a timesufllcient to cause said' body to exhibit a crushing strength. of notless than 25000 lbs. per sq. in. accompanied by a coefiicient of linearexpansion of about 2.0 to 2.5 times 10- per degree F.

4. In a process of forming a refractory body,

the steps of forming an intimate mixture of finely divided carbon,granular coke, substantially free from volatile matter, finely dividedclay and a quantity of water not substantially more than sufiicient torender. the mass extrudible under high pressure, shaping themass undersufiicient pressure to cause it to fiow, dryingthe so-shaped mass andheating it at a high temperature, about that of incipient vitrificationof the clay content, until the resulting refractory body exhibitssubstantially maximum strength and minimum coemcient of expansion.

5. In a process of producing a refractory body,

the steps of forming an intimate mixture of finely divided carbon,granular coke, substantially free from volatile matter, finely dividedclay and a quantity of water suflicient to render the mass extrudiblebut not sufficient to render it fluent and subjecting the resulting massto sufficient pressure to force the mixture of finely divided carbon andclay into the interstices between the granular coke and into the surfacefollicles thereof. I

6. In the process of producing a refractory body, the steps of forming abody comprising an intimate mixture of finely divided carbon andgranular coke, substantially free from volatile matter, finely dividedclay and a quantity of water suilicient to render the mass extrudiblebut less than suflicient to render it fluent, subjecting the mass tocompression suificient to cause it to flow, drying the mass and heatingit in an oxidizing atmosphere until the carbon content has been removedfrom a surface portion to a substantial depth.

7. In a process of producing a refractory body, the steps of forming abody comprising an intimate mixture of finely divided carbon andgranular coke, substantially free from volatile matter, finely dividedclay and a quantity of water sufficient to render the mass extrudiblebut not sumcient to render it fluent, subjecting the mass to sufiicientpressure to force the mixture of finely ivided carbon and clay into theinterstices be:- tween and into the surface follicles of the gran: ularcoke, drying the mass and heating it in an oxidizing atmosphere untilthe carbon has been removed from the surface to a desired depth.

8. In a process of making a refractory body, the steps of forming amoist, highly compact body of an intimate mixture of finely dividedcarbon, granular coke and finely divided clay, all said materials beingsubstantially free of volatile material, drying such body and subjectingit to an oxidizing atmosphere at a high temperature until the carboncontent is removed from an outer portion thereof to the desired depth,such temperature being low enough to avoid substantial vitrification ofthe clay content.

9. In a process of making a refractory body, the steps of forming ,suchbody, of a highly compact mixtureof finely divided carbon, granular cokeand finely divided clay, drying such body and removing by means of heatsubstantially all the adherent water and water of composition of theclay content.

10. Process of making a refractory, comprising the steps of forming anintimate mixture of finely divided carbon, finely divided clay andgranular coke, in proportion such that each particle of granular cokemay be thoroughly coated with a close mixture of finely divided carbonand clay, such materials being substantially free from volatile andreadily fusible substances, and sufficient water to render the mixtureextrudible but not suflicient to render it fluent, subjecting themixture to pressure sufiicient to cause it to flow, drying the resultingbody and heating it below the point of substantial vitrification of theclay content but high enough and for a sufficient time to removesubstantially allthe water of constitution of the clay content.

11. In a process of making a refractory body, the steps of forming suchbody of an intimate mixture of finely divided coke, granular coke andfinely divided clay, highly compacting such body, drying it and. heatingit at a temperature short of that required to cause substantialvitrification of the clay content thereof but high enough and for a timesufficient to cause the resulting refractory body to attainsubstantially its maximum shrinkage and exhibit high strength and low00- efiicient of expansion.

12. In a process of making a refractory body,

the steps of mixing in substantially dry state finely divided carbon,granular coke and finely divided clay, the quantity of clay beingsufficient to coat thoroughly all the coke particles, adding water andsubjecting every part or the mass to a smearing action, such as producedby pugging or kneading, whereby to coat the coke particles with claywithout damaging the coke granules, highly compacting the resulting masswhereby to form a semi-rigid, plastic body, drying said body and heatingit to ahigh temperature, but short of that of substantial vitrificationof the clay content for a time sumcient to cause the final product toexhibit a high strength and a low coefiicient of expansion.

13. In a process of making a refractory body, the.steps of mixing finelydivided and granular coke and finely divided clay, the quantity of claybeing sufficient to coat thoroughly all the coke particles, adding waterand subjecting every part of the mass to a smearing action, such asproduced by pugging or kneading, whereby to coat the coke particles withclay without damaging the coke granules,highly compacting the resultingmass whereby to form a semi-rigid, plastic body, drying said body andheating it to a high temperature, but short of that of substantialvitrification of the clay content for a time sufficient to cause thefinal product to exhibit a high strength and a low coefficient ofexpansion.

14. In a process of making a refractory body, the steps of mixing finelydivided carbon, granular coke and finely divided clay, the quantity ofclay being suflicient to coat thoroughly all the coke particles, addingwater and subjecting every part of the mass to a smearing action, suchas produced by pugging or kneading, whereby to coat the coke particleswith clay without damaging the coke granules, highly compacting theresulting mass whereby to form a semi-rigid, plastic body, drying saidbody and heating it to a high temperature, but short of that ofsubstantial vitrification of the clay content for a time sufficient tocause the final product to .exhibit a crushing strength of at least25,000 lbs. per square inch and a coefiicient of expansion of about 2.0to 2.5 times 10- per degree F.

15. In a process of making a refractory body, the steps of forming suchbody of a mixture, substantially free from volatile matter, of finelydivided and granular coke and finely divided clay, highly compactingsuch body, drying it, and subjecting it to a temperature of from about1800 F. to about 2800 F. for a time sufiicient to cause said body toexhibit a crushing strength of not less than 25,000 lbs. per square inchaccompanied by a coefiicient of linear expansion of about 2.0

to 2.5 times 10- per degree F.

16. Process of making a refractory, comprising the steps of forming anintimate mixture of finely divided coke, finely divided clay andgranular coke, in proportion such that each particle of granular cokemay be thoroughly coated with a close mixture of finely divided coke andclay, such materials being substantially free from volatile and readilyfusible substances, and sufficient water to render the mixtureextrudiblebut not suflicient to render it fluent, subjecting the mixture topressure sufficient to cause it to flow, drying the resulting body andheating it below the point of substantial vitrification of the claycontent but high enough and for a sufficient time to removesubstantially all the water of constitution of the clay. content.

MAHLON' J. REN'I'SCI-ILER.

